1. Field of the Invention
The present invention relates to heat sealable innerseals for use as secondary closures on containers, and a method for producing such innerseals.
2. Description of the Prior Art
Many products are distributed in plastic containers which include screw-on caps, snap-on caps or the like to form the primary closure of the container. In many instances it is desirable to provide a secondary closure for the container in the form of an "innerseal". Typically, an innerseal provides "tamper evidence" and acts as a vapor barrier to protect the product within the container.
One class of innerseals relies on a heat sealable polymeric layer which is bonded to the rim of the plastic container. These innerseals are positioned on the rim of the container and are passed through a radio frequency field which heat seals the innerseal to the container. After opening the primary closure the user may inspect the integrity of the innerseal, and reject the product if the innerseal shows evidence of tampering. Typically the user will pierce the innerseal and cut or tear away the innerseal material to gain access to the product in the container.
Examples of innerseals and related art include:
U.S. Pat. No. 4,684,554 to OuYang which teaches a heat sealable polymeric adhesive to seal an innerseal to a container such that at least 50% of the innerseal material is left on the lip of the jar as the cap is unscrewed and removed.
U.S. Pat. No. 4,666,052 to OuYang discloses a tamper indicating cap assembly having a transparent or translucent cap and an innerseal. When the cap is twisted open, the innerseal membrane is torn apart and evidence of tampering is visible through the cap.
U.S. Pat. No. 4,961,986 to Galda discloses a tabbed innerseal which allows removal of the innerseal as a unit. Although the innerseal of Galda may be easily removed, it is not necessarily tamper-evident.
U.S. Pat. No. 5,004,111 to McCarthy discloses a tabbed innerseal for removal of the innerseal by rupturing the heat sealing layer such that a substantial portion of the heat sealing layer is left on the rim of the container. The rupturing of the heat sealing layer permits easy removal of the innerseal, however the heat sealing layer is not particularly visible on the rim of the container.